Sadly there is no means to touchup the paint as you cut into the seam between the cover glass (which is painted) and the LCD panel.
Apple fuses the two together so dust or dirt does not collect between the glass plates. You would need to finish cutting around the cover glass clean it off and then repaint it. The rub here is you'll end up making a much bigger mess and you'll more than likely break cover glass or damage the LCD which would mean you'd end up replacing the complete assembly which would be quite expensive!
Bottom line here: Leave it alone! As you'll end up making a more expensive repair out of this!